As video appliances have become popular, demand has increased for image sensors such as CCDs, MOS CCDs, etc., of solid state image pickup devices. Conventionally, image sensors have been generally packaged using ceramics offering superior moisture resistance.
As the demand has increased as described above, however, image sensors have come to be used in a variety of configurations, and further it has become necessary to make the image sensor compact and lightweight. In order to satisfy the demand, therefore, and further in compliance with cost pressures, plastic packages have been used in place of ceramic packages.
Where plastic packages have been used for solid state image pickup devices having a large light reception portion such as image sensors, a unique problem must be solved.
Specifically, a solid state image-pickup device such as an image sensor, a phototransistor, a photodiode, or the like, performs photoelectric conversion on the basis of incident light, and the light reception portion thereof is transparently or light-transmissibly packaged.
In packaging the light reception portion with plastics, it is necessary that the package surface be smooth over the whole surface. If the package surface is not smooth or is damaged, scattering reflection of light occurs which scatters the light transmission.
Further, in pouring the synthetic resin, if dust is mixed in or if air bubbles occur, the quantity of light transmission is deteriorated. The scattering and decreased quantity of light transmission may be factors in disadvantageously reducing the sensitivity of the image sensor.
Moreover, it is necessary to improve moisture resistance in the device, a problem common to all semiconductor devices.
In the case where a plastic package is used in place of a ceramic package, it has been difficult to solve the problems described above.
Further, a photoelectric conversion element, including a bottom portion thereof, is integrally packaged with plastics except for its light reception portion. In this case, packaging often requires the use of a number of expensive metal molds.
While the above-mentioned package structure and package manufacturing method are suitable in producing a large quantity of photo semiconductor image pickup devices of the same structure, they require a number of expensive metal molds resulting in high production costs.
However, photo semiconductor image pickup devices are being used less than semiconductor devices such as amplifier circuits, comparators, etc. Further, as the performance, such as resolution, is improved, and as the devices are made smaller and lighter in weight, the devices have come to be used in a variety of ways.
By way of example, they have come to be used not only for video cameras but for medical appliances such as electronic endoscopes, and further for military devices.
In consideration of the increased use of such devices, it can be easily understood that not only is the function of such image sensors important but so are the external appearance and package structure thereof.
It is desirable to produce a small quantity and a variety of image sensors matched to the application for their intended use.
In the conventional structure and manufacturing method of image sensors, however, ceramics have not been suitable for the production of a small quantity and a variety of image sensors because a number of expensive metal molds are required.
Further, image sensors require a variety of clock pulses for image pickup, for pickup signal reading, and so on, and if functional improvement is desired (such as resolution) the number of external connection terminals for the supply of the clock pulses and for reading the pickup signal becomes large.
Conventional image sensors have a structure in which external connection terminals are provided on an outside surface of a package. Where the number of the terminals is increased, the intervals between the terminals becomes so narrow that an undesirable signal leakage, short circuit or erroneous mounting in soldering is likely to occur unless the package is large.
Further, good moisture resistance is required not only for image sensors but for all semiconductor devices, regardless of the package structure.
Also, it is important to have the photoelectric conversion element properly positioned in the lead-frame, and to position the glass plate properly with respect to the light receiving surface of the photo-electric conversion element.
Finally, if there is a gap between the photoelectric conversion element and the glass plate, the focal length to the object is undesirably increased according to the size of the gap.